On the origin of low‐energy electrons in the inner magnetosphere: Fluxes and pitch‐angle distributions

Abstract

Accurate knowledge of the plasma fluxes in the inner magnetosphere is essential for both scientific and programmatic applications. Knowledge of the low‐energy electrons (approximately tens to hundreds of eV) in the inner magnetosphere is particularly important since these electrons are acted upon by various physical processes, accelerating the electrons to higher energies, and also causing their loss. However, measurements of low‐energy electrons are challenging, and as a result, this population has been somewhat neglected previously. This study concerns observations of low‐energy electrons made by the Helium Oxygen Proton Electron instrument on board the Van Allen Probes satellites and also observations from geosynchronous orbit made by the Magnetospheric Plasma Analyzer on board Los Alamos National Laboratory satellites. The fluxes of electrons from ~30 eV to 1 keV are quantified as a function of pitch‐angle, McIlwain L parameter, and local time for both quiet and active periods. Results indicate two sources for low‐energy electrons in this energy range: the low‐energy tail of the electron plasma sheet and the high‐energy tail of the dayside ionosphere. These populations are identified primarily as a result of their different pitch‐angle distributions. Field‐aligned outflows from the dayside ionosphere are observed at all L shells during quiet and active periods. Our results also demonstrate that the dayside electron field‐aligned fluxes at ~30 eV are particularly strong between L values of 6 and 7, indicating an enhanced source within the polar ionosphere.

Analytical Chorus Wave Model Derived from Van Allen Probe Observations

“…The results of our chorus wave model are summarized as follows: In general, upper‐band chorus waves have lower amplitudes than lower‐band chorus waves. MLT dependences are different for chorus waves at midlatitude and low latitude. At low latitudes or near the equator, chorus waves are strong on the nightside and weak on the dayside; however, at midlatitudes, dayside chorus waves are stronger than nightside chorus waves. L ‐shell dependences are different for upper‐band chorus waves and lower‐band chorus waves at low latitudes, which may be explained by different energy sources for different bands and an upflow of warm electrons from the ionosphere (Denton et al, ). For the latitudinal dependence, the intensity of upper‐band chorus waves basically decreases with latitude. Intensity of lower‐band chorus decreases with latitude on the nightside but increases with latitude on the dayside. The Kp dependence is separated from the dependences on geomagnetic latitude, L , and MLT as a Kp scaling law.…”

Space Weather Effects Produced by the Ring Current Particles

“…IMPTAM provides nowcast of keV electrons comparable to the observations. A purely empirical model for ion flux and electron flux in the energy range ∼1 eV to ∼40 keV at geosynchronous orbit (GEO) was developed by Denton et al (2015Denton et al ( , 2017 based on a total of 82 satellite-years of observations from the Magnetospheric Plasma Analyzer instruments on Los Alamos National Laboratory satellites (http://gemelli. spacescience.org/mdenton/).…”

The Evolution of the Plasma Sheet Ion Composition: Storms and Recoveries

“…Since the energies of the 72 channels on the HOPE instrument are not fixed, all data used in the subsequent analysis are assigned to a grid that is fixed in energy with 72 energy bins, each evenly spaced (logarithmically) in energy, spanning the entire range of the HOPE instrument (cf. Denton et al, ).…”

“…These data provide the most comprehensive observations to date of ion composition in the inner magnetosphere. Surveys of the HOPE ions and electrons have shown the average behavior of the plasma under quiet, disturbed, and storm‐time conditions (e.g., Denton et al, ; Fernandes et al, ; Jahn et al, ). Such studies have provided the broad variations of the electrons and the ion composition with geomagnetic activity, MLT, and L ‐value.…”